Cost-effective climate control for hospitals

hospital applic ation guide
Cost-effective climate control for hospitals
• Munters locations
Munters is the world leader in dehumidification
Munters is the largest manufacturer of dehumidifiers in the world. Since developing the first desiccant dehumidifier in the late
1930’s, Munters has continued to innovate in the fields of dehumidification and energy recovery. Our long history and extensive
expertise in dehumidification makes us the premier choice for your dehumidification needs.
Controlling humidity in hospitals is obviously
important, but the fear of mold and bacteria
is not what is truly driving the requirement
for dehumidification equipment. Surgeons
are demanding cooler, drier operating room
conditions. Hospital administration has
prioritized indoor environmental conditions
not just for the safety of the patient, but also to
improve the efficiency and quality of work life
for the surgeon.
Many times surgeon discomfort is
obvious. The multiple layers of clothing, face
masks, hair covers, and protective gloves are
uncomfortable as they trap in body heat and
exacerbate perspiration. The key is to select the
most efficient climate control technologies to
eliminate wasted expense impacting operating
costs. Given the current climate of product and/
or service liability in the health care industry,
and the close tolerance for indoor conditions
specified by surgical equipment manufacturers,
hospitals have to invest periodically in upgrades
to existing HVAC systems or acquiring new
systems altogether.
Our extensive knowledge
and experience makes us
the premier choice for your
dehumidification needs.
Hospital Application Guide
1
Efficient ventilation solutions for hospitals
Outside Air
140
83°F, 133 gr/lb, 80% RH
120
90%
100
80%
80
70%
60%
Common Areas
60
75°F, 50% RH
50%
40%
Operating Rooms
40
60°F, 50% RH
20%
20
10%
10
20
30
40
50
60
70
80
90
100
Humidity Ratio Grains of Moisture per Pound of Dry Air (gr/lb)
Hospital engineers are challenged with the daunting task of employing HVAC systems that provide the proper amount of fresh outside air,
filtration, air changes, and temperature and humidity control. The proper selection and sizing of dehumidification equipment is critical for the
HVAC system efficiency and basic hospital operation.
110
Dry Bulb Temperature °F
Figure 1: Hospital design conditions
Condensation prevention
In hospital environments, it is critical that condensation be prevented.
omputers, electrical machines and lighting
C
all create high cooling loads. In order to offset
these loads, cold air is conveyed throughout
the building to maintain space temperature
set-points. Ductwork, distribution grills and
any adjacent surfaces will be cooler than air
temperature set-point and will be areas of
condensation formation if the temperature of the
surface is below the space dew point.
Ventilation air represents the largest potential
for introducing unwanted moisture into a space.
For example, in Greensboro, North Carolina,
each 1000 CFM of fresh air represents 7.1
gallons per hour of water relative to space
set-point of 60°F / 50% RH. Conventional
equipment that heats and cools air can remove
2
Hospital Application Guide
some of this moisture if the cooling load is
high enough. TMY weather bin data indicates
3623 total hours in Greensboro, NC where the
ambient dewpoint is above 55°F. The ambient
temperature is below 75°F 2,418 of these hours.
66.7% of the dehumidification season is cool
and wet simultaneously. During these times,
conventional equipment will be off, or cycling
on and off. This is the reason why the use of
thermostat controlled conventional equipment
commonly results in a building with high relative
humidity, condensation and mold issues. A simple
solution for maintaining accurate humidity levels
in the building is to control dewpoint in addition
to controlling temperature. By utilizing dewpoint
control the indoor environmental conditions will
be more manageable.
Surgical operations that require cooler space
conditions need substantially drier supplied air in
order to maintain 50% space relative humidity.
Common areas are generally maintained
at 75°F and 50% RH, which equates to a
55°F dewpoint. Operating rooms are often
maintained at 60°F and also must be kept at
50% RH, but this equates to a 41°F dewpoint.
This exact relationship represents the difficulty in
designing HVAC equipment to maintain cooler
operating room conditions. Both set points
equate to 50% relative humidity, but the cooler
set point requires substantially drier air.
1.
General comfort is significantly higher with
RH maintained below 60%.
2. Perspiration issues are minimized with RH
maintained below 60%.
3. Mold, mildew and fungi all feed on
moisture.
4. Higher relative humidity increases the
likelihood that condensation and fogging
will occur on magnifying lenses and
polished metal working apparatus.
OA pre-conditioning design guidelines:
1. Positively dehumidify all makeup air to required dew point.
2. Account for internal latent load. People load, open water and infiltration all represent internal
sources of moisture. Dehumidification equipment must supply air with a lower dewpoint than
the desired space dewpoint to support these internal loads- similar to cooling equipment that
must support loads from solar gain, lighting motors, by delivering air cooler than the space
temperature.
3. Reheat is required to prevent over-cooling the space. This is especially critical for operating
room applications (considering the conventional method for achieving 40°F dewpoint is to over
cool the air to 40°F). Reheat location can differ based on the hospitals needs and/or to prevent
duct condensation, but applying reheat at the site of the AHU restricts the individual control of
conditions in surgical suites.
Low-temp chiller approach
The low-temp chiller approach for dehumidifying operating rooms is to mix ventilation air with return air and then cool the entire air stream to 40°F.
Since 40° F supply air can not be achieved utilizing typical chilled water, this is generally a two step process. The first stage uses normal chilled water; for
example, 42°F that cools partially toward the 40°F air temperature goal. The final stage utilizes a lower temperature chilled water/brine mixture to achieve the
necessary 40°F air. Because this air is too cold, reheat is applied as needed at each zone to maintain temperature set-point. To simplify this approach, designs
often use a one stage approach where the entire dehumidification process is accomplished with one large coil served with 35°F water/brine mixture.
Microbiological growth
Many bacteria flourish in humid air. According to a study done by Pennsylvania State University, the
bacteria responsible for Legionnaire’s disease (Legionella pneumophila) survive best at a Relative
Humidity of 65%. At 35% RH, the bacterium dies quite rapidly. Many viruses also thrive in high
humidity. The Polio virus not only survives, but multiplies when air is above 80% RH. Fungi and dust
mites also thrive in humid building materials, which can lead to musty odors and respiratory problems
associated with sick building syndrome. The high humidity in ductwork downstream for cooling coils is,
unfortunately, an ideal environment for these organisms.
Heating Coil
(Winter)
Dehum Cooling Coil
Stage 1
Dehum Cooling Coil
Stage 2
Challenges with this approach are:
1. A low temperature chiller has a 20% first cost premium compared to an equivalent tonnage
Figure 2: Low-temp chiller approach
Low-temp chiller approach
standard chiller.
35˚F
42˚F
2. The KW/Ton is approximately 22% higher for a low temperature chiller vs. an equivalent
Outside Air
Low Temp
Chiller
45˚F
52˚F
Chiller
4,000 cfm
Plant
83˚F, 133 gr/lb
tonnage standard chiller.
3. 40°F is the lowest dew point that can reasonably be achieved without the risk of freezing the
Supply Air
Mixed Air
40˚F
chilled water coil. All of the air must be cooled to this dew point to achieve the desired space
55˚F
68˚F
36.5 gr/lb
71gr/lb
64 gr/lb
humidity and substantial sensible cooling must be consumed before any moisture is condensed.
Return Air
8,000 cfm
4. Substantial reheat energy is required to prevent over-cooling of served areas.
60˚F, 40gr/lb
Reheat Boxes
5. Either a separate chiller is required or the whole chilled water system needs to be low temperature type.
57˚F LAT
6. Conveying cold saturated air from the main air handler to reheat boxes will challenge insulation
Surgical
Surgical
Surgical
Surgical
to prevent condensation on duct exteriors.
Suite 1
Suite 2
Suite 3
Suite 4
7. Any apparatus, such as filters, will create condensate down stream of the chilled water coil.
Saturated air moving across any pressure loss device will condense.
8. 35°F water/brine mixture requires better piping insulation package in order to prevent
condensation.
9. 35°F water/brine mixture has a higher probability of leaking at connection areas.
10. The air handler system for the low-temp chilled water approach should include construction that limits through metal from the inside to outside. If
mounted inside or outside, the air handler surrounding dewpoint will often be higher than 40°F, and any through metal area will sweat profusely.
Air handler door frames, wall panels and through connections should include a thermal break. This construction is not conventional and will be more
expensive compared to a typical air handler.
Bacteria growth caused by
saturated duct conditions will be
significantly minimized with a
desiccant air handling system.
Hospital Application Guide
3
Desiccant dehumidifiers
Desiccant dehumidifiers utilize a desiccant wheel
to provide dehumidification of the supply air.
The operation of a desiccant wheel is based
on the principal of sorption. Sorption is the
adsorption or the absorption process by which
desiccant removes water vapor directly from
air. Most commonly, desiccant is embedded
within a rotary bed (rotor or wheel). The wheel
is split into two sectors; the supply air stream
and reactivation air stream are continuously
rotated in order to provide the dehumidification
process. Once the wheel absorbs moisture, the
moisture must be driven off of the wheel during
a "reactivation process." The desiccant wheel
rotates into a secondary air stream (reactivation
air) where water vapor is transferred to heated
air, and exhausted.
Reactivation temperature can range from
110°F to over 300°F depending on application.
Generally, the drier the air requirements,
the warmer the reactivation air must be. As
supply air is dried through the desiccant, it is
simultaneously heated.
For example, 55°F saturated air (64 gr/lb)
entering will leave at 97°F and 29 gr/lb. Rotor
speed is generally eight revolutions per hour.
Most of the heat associated with the drying
process is converted latent energy.
Since hospital applications require
cooler temperatures and lower
dewpoints, desiccant technology is an
optimal method to achieve operating
room conditions and helps reduce the
cost of equipment investment.
Note the following:
1. The cost to operate a desiccant
approach will be approximately
40% less then the low temp
chiller approach.
42˚F
Supply Air
57˚F
36.5 gr/lb
Hospital Application Guide
Mixed Air
70˚F
36.5 gr/lb
52˚F
97˚F
29 gr/lb
Outside Air
4,000 cfm
83˚F, 133 gr/lb
55˚F
64 gr/lb
Reheat Boxes
57˚F LAT
Surgical
Suite 1
Surgical
Suite 2
Surgical
Suite 3
Surgical
Suite 4
Return Air
8,000 cfm
60˚F, 40 gr/lb
Figure 3: Desiccant dehumidification approach
2. Desiccant pre-cooling and final post cooling requirements are achieved using standard
temperature chilled water. The added cost for a special low temperature chiller is removed. The
inefficiency associated with a low temperature chiller is also removed.
3. Since desiccant dehumidification can easily achieve dewpoints lower than 40°F, only a portion of
the total supply air only needs to be dehumidified. This allows for greater system design flexibility.
In this example, only the outside air requirements are dehumidified. All the work associated with
sensibly cooling the supply air to dewpoint is removed from the equation.
4. Cooling fluid is warmer reducing the chance for pipe condensation.
5. Cooling fluid does not require brine mixture, removing the added propensity for leaks, and
removing the cost of maintaining correct fluid chemistry.
6. Supply air is not over-cooled dramatically reducing the reheat energy required at each zone.
7. Conveyed air is not cold and saturated, which reduces chance for duct condensation, and
condensation across pressure loss apparatus within the supply duct.
Conclusion
The medical industry is advancing at a quick pace, and so are the dehumidification technologies. It
is critical that design engineers identify the required space temperature and dewpoint conditions to
determine what dehumidification equipment will meet the needs of the hospital. When choosing the
equipment, in addition to precise space condition control, engineers should also consider methods to
improve the total operation of the hospital. With increased utility costs, design engineers are opting
for more reliable and energy efficient dehumidification options. Dehumidification of surgical suites
is achievable with many technologies, but with the growing demand for colder and drier operating
rooms, selecting the proper equipment is more important than ever. Choose equipment wisely, it is not
only important for the hospitals bottom line- your life may depend on it.
4
42˚F
Chiller
Plant
52˚F
Pre-Cooling Coil
Drive Motor
Figure 4: Desiccant dehumidification approach
Desiccant technology is widely viewed as the most viable method to generate air lower
than a 45°F dewpoint. In fact, for applications requiring dewpoints below 35°F, desiccant
dehumidification is the most reliable andDesiccant
modern
approach utilized.
dehumidification approach
Desiccant Wheel
Pre-cooled Outside Air
Heating Coil
(Winter)
Dry Air
Desiccant approach
Post-Cooling Coil
(Sensible Only)
Wet Air
Reactivation Air
Munters is a global leader in
energy efficient air treatment solutions
Using innovative technologies, our expert engineers create the perfect climate for customers in a
wide range of industries, with the largest being food, pharmaceutical and data center sectors.
Munters has been defining the future of air treatment since 1955. Today, manufacturing and
sales are carried out in 30 countries by around 3,000 employees. Munters reports annual net
sales in the region of SEK 4 billion and is owned by Nordic Capital Fund VII.
For more information see www.munters.com
Australia Munters Pty Limited, Phone +61 2 6025 6422, Fax +61 2 6025 8266, Austria via sales organization in Germany, Brazil Munters Brasil Industria
e Comercio Ltda, Phone +55 41 3317 5050, Fax +55 41 3317 5070, China Munters Air Treatment Equipment (Beijing) Co., Ltd., Phone +86 10 80 481
121, Fax +86 10 80 483 493, Denmark via sales organization in Sweden, Finland Munters Oy, Phone +358 9 83 86 030, Fax +358 9 83 86 0336,
France Munters France S.A., Phone +33 1 34 11 57 50, Fax +33 1 34 11 57 51, Germany Munters Euroform GmbH, Phone +49 241 89 00 0, Fax +49
241 89 00 5199, Indonesia Munters, Phone +62 21 9105446-7, Fax +62 21 5310509, Italy Munters Italy S.p.A., Phone +39 0183-52 11, Fax +39
0183-521 333, Japan Munters K.K., Phone +81 3 5970 0021, Fax +81 3 5970 3197, Kingdom of Saudi Arabia and Middle East Hawa Munters, c/o
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Munters (Thailand) Co. Ltd., Phone +66 2 645 2708-12, Fax +66 2 645 2710, United Kingdom Munters Ltd, Phone +44 845 644 3980, Fax +44 845
644 3981, USA Munters Corporation Fort Myers, Phone +1 239 936 1555, Fax +1 239 936 8858, Munters Corporation Mason, Phone +1 888 335
0100, Fax +1 517 676 7078, Export & other countries Munters, Phone +46 8 626 63 00, Fax +46 8 754 56 66.
Your closest distributor
Munters Corporation
Tel: (800) 843-5360 E-mail: [email protected] www.munters.us
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